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Has a jet "engine" ever been made that only uses the thrust from the bypass air and doesn't have a combustion chamber?
I recently have been looking at different types of jet engines and came to this thread wherein they talk about how most of the thrust from airline turbofan engines (high bypass) comes from the bypass air and not the combusted air coming out of the internals of the engine.
So my question is, has there ever been a sort of fan engine used that only uses bypass air and the fan is run by a separate engine? Would this even be viable?
Edit:
Basically a turbofan that just uses the power of the increasing speed of the air through the smaller space, no combustion (other than the standard piston engine/electric motor/whatever).

I'm not sure what you're looking for. It sounds like you are just describing a turbofan.

@Thomas except that it would be hard to have a turbofan without a combustion chamber like the title says. Closest would be a turboprop where the exhaust creates very little thrust.

I'd suggest much more practical questions would be "can you remove the combustion chamber from a jet engine" or "What's the limit to how high of a bypass ratio you can get?"

I was thinking the same thing about the turboprop, but it does have a combustion chamber so it isn't exactly what I'm looking for. If that is the closest thing then I guess the answer to this question is probably just no.

It's not really bypass air if it isn't going into the chamber though.

@CodyP Yes those questions are pretty much what I'm getting at. If there is a limit to the bypass ratio then I think that'd mean there can't be a turbo fan without the combustion chamber/high pressure area of the engine, right?

Oversimplifying thermodynamics for a moment, you cannot get work from combustion without high pressure. However, any electric plane would not have a combustion chamber, due to the lack of combustion to begin with.

I've just edited in a drawing of what I mean. Not without combustion at all (so laws of physics are intact) but without a jet combustion chamber. So the power comes from a standard rotating engine shaft, without the extremely high fuel consumption that standard jet engines have).

I think you're talking about a perpetual motion machine which...I don't believe is physically possible.  You can't generate enough force from the incoming air in order to have enough force to force the air in.  You'd be going against the laws of physics at that point.  Somewhere in there something external has to be adding power to the system to make it work.  Engines, technically, only convert energy, they don't create it (which, you know, is impossible.)

No below you'll find the answer to my question. I was talking about a ducted fan. What is this about a perpetual motion machine? The drawing and my description show an engine that turns the fan blades, converting chemical energy to mechanical. By your description of engines they shouldn't be able to do anything just because they don't create energy.

Well what you are describing is a ducted fan.  They are common on RC aircraft with the fan driven by either a gasoline engine or electric motor.
On large scale applications like an airliner, you have to find a source of power for the fan that is 1) compact 2) light weight 3) delivers a very high specific power and 4) draws energy from a reservoir with a high energy density, all while remaining 5) extremely reliable and 6) safe.  For these kinds of applications, you really can’t currently do better for this than use a kerosene fueled gas turbine engine to drive the fan.  And that's all a high bypass turbofan really is - just a gas turbine powered ducted fan.

Thanks for the detailed explanation. That last sentence is a great way of summing it up for me and the engineering behind the turbofan engine makes so much sense now. Power the fan with the air that comes in, duh. So simple (conceptually) yet so smart. Thanks again

@TrapAlcubierreDrive. No, you cannot "power the fan with the air that comes in". You need to supply additional energy to gain thrust, because the incoming air needs to be accelerated to cause an increase in momentum, which gives you thrust. You need a motor of some sort. Electric, diesel, gasoline, kerosene. Pick any one.

@Penguin: Well, it is technically possible to power a jet engine from a power source that doesn't require siphoning off any of the intake air (such as an electric, nuclear, or nuclear-electric motor), which might have been what TrapAlcubierreDrive was thinking of...

The UL-39 ALBI is a prototype ultralight that uses a ducted fan driven by a reciprocating motorcycle engine. The idea is that for the levels of power needed by such a small aircraft, piston engines have better thrust-to-weight and thrust-to-cost ratios.
You can also find piston-driven ducted propellers on some airships, mainly so they can vector the thrust for steering.
There is also the case of the F-35 STOVL. Here, the lift fan is driven by a jet engine not in the flow path; this is so you don't need a dedicated engine for that fan.

That's it! The ducted fan. It seems really obvious when I don't talk about jet engines in the same sentence. Sorry for anyone that got really confused by my wording, I'm new to this stuff.


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Would a ducted fan with a nozzle like a jet engine have more thrust than a normal ducted fan?
I'm trying to design a miniature ducted fan engine for a small project, but I'm not too sure how much contraction should happen between the fan and the end of the engine, if at all.
Engines like this  or this look like they have very little contraction at all, but why not use the pressure created by the fan and contract the space making the output velocity higher?
This is the same sort of principle behind the bypass air of a turbo fan engine and I don't see why not to use it.

I do mean the nozzle, yeah. Even if they don't need them would it increase thrust?

I edited it. Not sure if it will get an answer at this point since it's an older post.

I’d suggest this paper as a starting place.  https://proceedings.asmedigitalcollection.asme.org/data/Conferences/ASMEP/83879/V001T01A020-83-GT-42.pdf

Are we talking about small in terms of human scale or small like a model airplane?

but why not use the pressure created by the fan and contract the space making the output velocity higher?

That is exactly how the pressure energy added by the fan is converted into thrust. Thrust, after all, is the product of the speed increase between free stream and exit flow, mass flow and nozzle area.
That real jet engines don't show so much contraction is due to the expansion of the core gas flow from heating. If you don't add heat, your exit area should be quite a bit smaller than the entry area.
If by "normal ducted fan" you mean one where the duct is simply a cylinder of constant diameter, then yes, a properly designed nozzle will create more thrust.

Thank you for the answer. Is there some source you can send me to for how to properly design the nozzle for this?

@TrapAlcubierreDrive: Uh - no, I'm afraid. Maybe there is something, but I don't know it. You should be able to calculate the speed increase and from that the area required for equal mass flow. Keep in mind that the growing boundary layer will increase the area slightly in flow direction. Ideally, half of the contraction happens ahead of the fan and the other half behind it.

@PeterKämpf: Since the efficiency of a ducted fan is 2*w0/(w9-w0) where w0 is the speed of the ambient air and w9 is the exit velocity of the ducted fan, increasing the exit speed with a nozzle would lower the efficiency. To your point that turbofan bypasses don't have a nozzle because of the hot exhaust would mean that something like the airbus e Fan should have strongly converging path, which it doesn't. https://media.wired.com/photos/5a5c7c7ea92f71125d0f9801/16:9/w_1280,c_limit/P1200929.jpg

@hph304j The e-Fan does not add much energy to the flow - what do you expect from electric propulsion? The jet contraction is much higher with the energies needed to power an airliner, so that comparison is not valid. Next, take a straight cylinder and accelerate the flow inside. Look at the efficiency. Repeat with a properly converging cylinder. Of course does some contraction improve efficiency and with it thrust.

@PeterKämpf: If you could please provide me with some sources for your last statement about the straight and converging cylinder, I would highly appreciate it.

Depending what you mean by a smaller unit. For some time now I have been studying and testing 'electric ducted fans' where gas velocities are less than 100m/s and RE less than 150k. I have manufactured my own and tested numerous units from various sources. I am a retired production engineer with the best part of 30 years dedicated to gas turbines including pure jet, low and high bypass, shaft engines both for flight and static. These little horrors have left me at times baffled. Nothing I have read pans out. First measuring gas velocities from the entry to the exit, not once have I found a significant change in gas velocity after the entry to the fan. Just decay. They do not operate in any way like a full size high bypass fan. It appears only Guy Lussacs gas laws can be applied. Any nozzle other than the vane section reduces thrust for a given power input. More power higher rpm, creating a greater reduction in pressure at the entry to the fan compensates. So far, I have found, only the shape of the entry to the duct can improve static thrust for a given power input. I realise now that I have years of work to provide a comprehensive guide to small low velocity fans. The next step is to build a small dynamometer to ensure I know the power input to the fan and then a small wind tunnel. There is much more I could say but at this stage all I will say is that they are pressure difference propulsive units with very little momentum change. I have thousands of measurements of thrust, gas velocities, power requirements, pressure measurements, etc.
Finally good luck in designing a minature high bypass unit. I imagine you are trying to produce a minature gas turbine driving your fan. There is a good deal out there to help you but the bypass fan may not operate in quite the way you expect.

It all depends upon the configuration of the diffuser for the fan but the answer is not necessarily.  For a typical high bypass turbofan on a transonic aircraft application, it will use a fixed geometry diffuser (nozzle) for both fan and gas core exhaust with the nacelle.  P&W and GE engine’s have opted to use a separate cool section and hot section diffusers.  Rolls Royce seems to prefer a single diffuser which combines both the fan and gas core exhaust prior to exiting the nozzle for noise reduction reasons.  Both designs are very efficient for their appropriate applications.
High bypass turbofans have exhaust flow speeds in the high subsonic and transonic regions but do not require a fixed or variable convergent-divergent diffuser for supersonic gas flow.  The reasons are primarily that it is 1) less fuel efficient for a subsonic application and 2) supersonic exhaust flow is extremely noisy and limits the airports where the jet could fly into due to noise restrictions.
Your exact design for your particular diffuser is going to depend on the configuration of the engine as well as the installation constraints.  You’re also going to have to calculate the impulse the engine needs to provide and this is going to determine the exit speed of the gas through the diffuser.  It’s going to be a little more involved than simply copying an existing design and making something that looks similar.

Thanks for the response. For a small ducted fan engine, like the one I'm making, is the fan not enough to compress the air? Is a diffuser really necessary for it? I might be totally confused as to what you're referring to with the diffuser because I just googled the part schematic of a jet engine and it seems like they are stationary blades that further compress the air. You say "fixed geometry diffuser (nozzle)" though, so are you saying the nozzle and the diffuser are the same thing?

Nozzle and diffuser are interchangeable terms.  And yes, a diffuser is an integral part of the system, as it converts the enthalpy of the airflow added by the fan into kinetic energy, creating the reactive thrust.

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Why aren't any wingsuits able to sustain flight?
I'm aware that under zero power it is a glider, but there are gliders that sustain flight and have enough lift to climb etc (Edit: this is not always true. See below answers for why). So, would it not be an interesting idea to make a wingsuit that you can use to climb and not just fall?
With longer wings could it be done? Or maybe a longer airfoil?

Yes, it's called a hang glider.

Many years ago, a friend of mine used to joke that people flying hang-gliders would eventually invent the glider. Looking at the rigid wings and all the electronics you see these days, he was not far from the truth.

Obligatory mention of the fictional "wingsuit" which used lighter than air gas to inflate the suit enough, supposedly, to enable a sort of flight. http://dc.wikia.com/wiki/Max_Bine_(Earth-Four)

Given sufficient lifting air, anything can sustain flight.  The only trick is finding a location with enough lift -- perhaps near a tornado?  ;)

There are very small jets that for hype-related reasons are called wingsuits. As current jet technology (and propeller technology) is easily capable of producing (from a human-portable frame) enough thrust to lift itself and a human-sized load, there is no obstacle to creating a true powered wingsuit. The reaction surfaces are very small in relation to the combined mass and necessary speed, so it will not be a swooping-soaring kind of flight, and more ballistic — unless you opt for vectored thrust, which is cheating.
EDIT: I just realized you were asking about unpowered flight. The glide ratio on a wingsuit is much too bad for that: you'd need hurricane-strength updrafts. A normal glider has about 500kg of total mass, and <20m wingspan for a glide ratio of about 40:1, which is just enough to soar in good thermals. To get that on a wingsuit (which might weigh, with occupant, 100kg) you'd need about a 5 meter wingspan (but this does not take into account that the Reynolds numbers start working against you as you scale down - Andean condors are 15kg @ 3m wingspan!). This might be achievable with tensairity or some other lightweight wing concept. You'd need something to take the brunt of the lifting force for you, while retaining the intuitive grasp on the lifting surfaces you get in a wingsuit. Should be doable, but I guess the engineering on something like that is too expensive to have been done by enthusiasts.

What kind of Reynolds number effect do you have in mind at these scales? Do you belive the skin friction / form drag ratio is significantly larger for a human size object than for a glider aircraft sízed object?

What you need to effectively gain altitude in thermals is a low sink rate.
A good L/D is what you need between thermals so that you can find the next thermal before running out of altitude, but it's not a requirement for gaining lift.  If you're willing and able to stay in a thermal for the entire flight, then you just need a low sink rate.

That said, I'll bet that wingsuits have unfavorable sink rates for thermalling.

@VladimirF : A human is about 5 times shorter than a glider, and certainly not faster (in the glider-wingsuit), so the Reynolds number would be about five times lower, so we're very near the 150 000 that separates the two regimes of airflow.
WayneConrad : while max L/D and min sinkrate are not reached at the same velocity, planes with a good L/D and planes with a low sinkrate are usually very similar (glider often take on water to finagle the specifics of L/R vs. sinkrate, but they stay the same aerodynamically.

I don't think the chord length of the wing is that different. The length of the tail is irrelevant.

I'm aware that under zero power it is a glider, but there are gliders
  that sustain flight and have enough lift to climb etc.

This statement is a bit incorrect. Gliders don't climb like aircraft as they are constantly falling to the ground unless they catch a thermal, wave lift or ridge lift, in which case they can ride the updraft to gain altitude. In theory, a wingsuit could do that if you could maneuver to stay in the thermal but wingsuits are not maneuverable like a glider and tend not to have nearly the glide ratio of a glider so they sink far faster than a thermal could cary them up.
There is an interesting discussion on it here.

Oh I see. I guess I misinterpreted what someone said on this forum. Thanks for clearing that up.

An unsuited human can ride an updraft too.  At least if that updraft is from a transport aircraft propeller under a floor grating...

I thouugth it was much about fall rate than glide ratio. Best glide ratio is generally achieved at a greater speed than lowest fall rate.

"wingsuits are not nearly as maneuverable" i strongly disagree on this one

As an ex-hang-glider pilot...
Two other answers have covered the basic concept of gliding - namely that you're constantly descending, and to stay aloft you need to be in air that's rising faster than you're descending. Early hang gliders and paragliders had no problems staying up in normal ridge lift with glide ratios of 7ish:1.  Before that, they were just an exercise in top-to-bottom "sled rides".
EDIT TO ADD EVIDENCE: According to Geoff Broom, the first hang-glider flown in Britain in 1971 had a glide ratio of about 3:1 in flat air, or 5:1 in ground effect from flying close to the hill, and this was strictly limited to top-to-bottom flights. By 1972, pilots on Broom's gliders were starting to manage sustained soaring flights in ridge lift.  The Skyhook Mk3 hang-glider plans recommend learning on a hill with a 5:1 slope, requiring the glider to have at least this glide ratio or better.
In more exceptional weather conditions, of course, you can get away with worse glide ratio; in fact you may want to. Most hill pilots (myself included) have had the experience of the wind picking up during their flight and having to pull on full speed (essentially a dive) in order to get back down to the ground against the rising air. So it's theoretically possible for a wingsuit to stay up in those kind of conditions.
And in the most extreme cases, it may simply be impossible to get down. I've read of paraglider pilots caught in the updraft from a cumulonimbus formation, where they have literally pulled their canopy in around themselves and were still going up, because the cu-nim updraft was stronger than gravity.
What other answers haven't covered though is that you also need to be able to land. If you can't flare to a landing below running speed, then you have problems! Typically a hang-glider has a stall speed of 15-25mph, and from that speed can be flared to near-stationary on landing. A wingsuit flies at around 60mph, and cannot be flared in anything like the same way. A good wingsuit pilot probably could stay aloft on a ridge in high winds, but he'd need to pop a chute to land - and parachutes and high winds are not a healthy combination.

Because the glide descent ratio of a wingsuit is around 2:1 vs a well designed sailplane exceeds 40:1.  This very gradual descent rate allows the sailplane to take advantage of normal, commonly encountered thermals in the atmosphere and gain altitude when in them.  Thermals do alter the rate of descent for a wingsuit as well but is generally not powerful enough to allow the jumper to gain altitude.
It is theoretically possible for a wingsuit rider to ride powerful thermals or strong updrafts such as those encountered in the mature stage of a severe thunderstorm.  However the dangers associated with flying in violent weather like that deter any attempts.

Cross country competition gliders like the Nimbus 4T with a 26.5 meter wingspan have glide ratios of 60:1.

A favorable glide ratio is not needed for gaining lift.  What's needed for gaining lift is a suitably low sink rate.  But I think a wingsuit probably has a lousy sink rate.

@WayneConrad Minimum sink is indeed the issue, but the only way to get a low sink rate with a low glide ratio is to go slowly, and wingsuits do not fly slowly. Fair-weather thermal soaring with a 2:1 glide ratio would require an airspeed around 10 knots.

The human body isn't strong enough to sustain flight in a wingsuit, without adding structural elements to make the wing independent of the human body.
Current wingsuits have wings that are too small for level flight. To get more wing area, you need to make the wings longer. But this increases the force exerted on the wing. In a wingsuit, the user has to push his arms and legs down to counteract the upward force exerted by the airfoil. For a wing that allows level flight, the user has to push down with a force equal to his own weight. Even strong athletes have trouble doing this for more than a minute or so.
You'd have to add two spars across the wing that take most of the load. The spars would be attached to the user's torso and transmit the forces without requiring the user to keep his muscles tensed up.
The wing would then allow the user to use his arms as control surfaces. I've never seen a wingsuit design like this though.

Thanks for the info. I guess that's why the guys with the jet suits have wings attached to them not as a part of them.

This has a good example at the 2:15 mark. The glider has plenty of control for a landing. He is close enough but has to maintain a speed that is WAY TO FAST to land.

shows an example of a wingsuit jumper entering a plane, notice the speeds and angle of the plane.
Basically there just isn't enough lift generating surfaces to go slow enough to land.
Same is true for a climb. You just need more lift generating surface then is available. That said, it could work, in an insanely strong updraft, but it probably wouldn't be very much fun.

A regular skydiver in a track (the same body configuration as a ski jumper) has an L/D of about .5 to 1.   Wingsuits improve the L/D to 1 to 1, which means a jumper weighing 200 lbs is generating about 200 lbs of drag at his gliding speed.  Just to maintain level flight he'd need 200 lbs of thrust from a power source.

So 200 lbs of thrust for 200 lbs of drag. Why is it that number? Is it always how it works out that the drag force equals the thrust required?

If the total lifting force in steady state flight is equal to the all up weight, and knowing the L/D ratio, then drag is the product of the L/D ratio applied to all up weight.  A sailplane with an L/D of 40, with an all up weight of 700 lbs, when flying at its max L/D speed will have total drag of 1/40th of its all up weight, or 17.5 pounds of drag.  17.5 pounds of thrust would be required to maintain level flight.   A wing suit with an L/D of 1:1 will require the same thrust as the all up weight to maintain level flight.

There was a guy with a wingsuit that installed a Jet Cat micro turbojet on each foot and it looked like he was in level flight but I don't think those engines made quite enough thrust and I suspect he was still descending but gently.

The wing surface area is too small to support the weight of the human pilot. Wings that small simply can not generate enough lift to sustain unpowered flight.
Below is the engineering "lift equation" you seek.

Here is the NASA article that describes how lift works in detail.

If you have enough power, it doesn't matter how small the wings are.  Without power, a wing or lifting body, no matter how small, can still glide at some angle less than straight down.  A bare human body in a track position still has an L/D of .5 and can attain 60 mph horizontal speed at terminal velocity.  This is one of the major risks in skydiving relative work, running into each other while tracking.  The issue is how steep the glide, or how much thrust is required to fly level if there is an engine.

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Why aren’t airliners powered gliders?
The Perlan high altitide glider project has the following stats

This suggests that a glider / high altitude airliner could be economically viable and save a lot on fuel at 60000ft.
I realize this is not a complete picture, but it seems compelling. How to fully analyze this? Please list steps.
There have been a number of military gliders that are large
https://en.m.wikipedia.org/wiki/Military_glider

@ralph j. This is not homework. Is self assigned.

Because gliders are slow, and the appeal of commercial air travel is crossing the country in 4 hours.

"crossing the country in 4 hours". Well that's not a very difficult goal to achieve for most of the world :-) We just need to slow down a bit.

@mins: In which case you could just take a train :-)  Or a ship, if you're crossing the ocean.

@abelenky look at the graph of speed. Gliders can be fast

The graph says Vne at FL300 to FL400 is 200 to 250 kts while airlines easily do 500-600 kts.  That does not look fast to me.

They are powered gliders. They are just much better at the "powered" part than at the "gliding" part.

Why aren’t airliners gliders? Because it takes lots of power to move a hundred or so people across the country and gliders are by definition unpowered.

Powered gliders exist. Also with a much longer glide distance aka lower wind resistance.

@mins airliners have a glide ratio much lower than that defined for gliders.

@JosephHobbs: Yes, as I wrote... they are optimized to lift 200 tons and fly at Mach .82. Else they are able to glide very well.

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Can airline ignore or get exception from V1 and other safety rules?
In this famous video with not to good quality now

 I don't believe this IL76 was able to takeoof if the engine failed. Are the rules ignored? Or it's possible to get permit takeoff without V1 and any consideration for engine failure on multi engine airliner?
Update:Ok V1 maybe is not a rule. It's a number that you get after application of certain rules. But MEP aircraft doesn't have V1 and single engine aircraft as well. They all operate and even can carry people.
Maybe it's possible get an exception to operate ME turbine aircraft without consideration of an engine failure? For example runway is very short or you are heavily leaded and aircraft will not climb at all with -1 engine.
I was not asking about the V1.
Maybe there is an airport somewhere very high with 40 degrees outside, short runway and down slope. Guys have IL76 fully loaded. They see that there is no way they can takeoff applying standard safety rules. But they run calculation and they see that if they use 100% of runway for take off run they will get 1% climb gradient with all engines on full power. If you want to depart very much maybe it's possible to go to aviation authority and ask for a special permit?

What evidence is there that V1 was ignored? 4 engine aircraft have very different takeoff profiles compared to 2 engine aircraft. Heavily loaded 4 engine aircraft routinely use more runway than 2 engine aircraft.  V1 is just a speed where you can decide to stop on the remaining runway.  Vr is when you rotate and has nothing to do with the amount of runway remaining.

V1 is simply the point at which you are committed to taking off, regardless of engine failure. Because of the long take-off run and possibly short runway, they may have hit V1 very early on and elected to continue. The video you show is Australian, but I don't know of any "permit" process for take-offs. The worst these guys may have done was violate the Ops Spec manual from the operator. At least in the U.S., you are allowed to use as much available runway as you want.

V1 is not a safety rule, and as such there is no such thing as getting an exemption from V1. Just like the stall speed is not a safety rule, and you can't get an exemption from stalling...

"I'm running out of film. I don't know if I'll have enough to film the crash." That is a great line!

I wonder if this was a reduced thrust (flex temp) takeoff?  That'd explain eating the entire runway, as your all-engine accelerate-go becomes the limiting factor here -- if you lose an engine above V1, you simply put TOGA power on the rest, leading to an engine-out accelerate-go that's shorter than the all-engines case.

If you use flex temp there is no requirement to put TOGA. Airplane should be able to takeoff with the power available. Reduced trust takeoff means that you have TO MUCH power for that runway and you can save engines.

I’ve met the ATC who filmed this and he said it was a military flight, and the pilot “knew exactly what he was doing”. Whether he knows that as a fact or not I don’t know...

To answer the question as asked, no I've never heard of an airline "ignoring" V1.
To address the implicit question, I have no idea what the story is behind that IL-76 operation shown in the video, but I could creatively come up with all sorts of possible explanations for the takeoff roll that essentially matched the available runway: power not set correctly, takeoff data computed incorrectly, poor pilot technique, unexpected tailwind, aircraft loaded heavier than expected, or maybe that crew DID decide that it was so important to get home that they were willing to accept an absurd risk.  But I wouldn't take ONE video without explanation of "what really happened there" as any indication of what airlines in general will do.
At its most basic, V1 is simply the point at which you transition from a "stop" mentality to a "go" mentality: if something goes wrong PRIOR to V1, we'll stop; if something goes wrong AFTER V1, then we'll go.  Now, there are LOTS of things that complicate that discussion... not everything that can "go wrong" is the same: at 80 knots, getting an "anti-skid fail" light is probably not worth aborting for; at 80 knots, getting a loss of all generators probably IS worth aborting for (assuming that V1 is well above 80 knots).  Just below V1, losing an engine IS something you'll stop for; losing one generator or one hydraulic system might not be.  And this is all dependent on the aircraft... in the C-130, we were pretty stop-oriented, and we'd stop for all sorts of things immediately prior to V1 that in the 737 -- a much more go-oriented aircraft -- we'd take airborne.  The difference being, you can stop the Herk pretty quickly & with a comparatively low risk of problems; a high-speed abort in the 737 (as in many jet aircraft) is much more of a big deal.
All that said, though, there is always a speed below which you'll stop, and above which you'll go.  If an engine flames out at 20 knots, you'll stop in nearly any scenario I can think of (that doesn't involve bad guys storming the airport).  In the Herk, it was common that your accelerate-stop speed was above your rotation speed, so V1 was essentially at rotation.  But there was always some speed where your default choice between stop/go changed over.
You might "ignore V1" by simply saying that once takeoff power is set, we're going to continue regardless, but that's just bad decisionmaking by the crew, and not the sort of policy that I could envision ANY airline ever making.  (Again, the case of mortar shells falling closer & closer to the aircraft & bad guys overrunning the airport might be an exception to this... take our chances with the ground rather than with the bayonets.  But the outlandish nature of this exception illustrates how rare it would be to "ignore V1" in any considered scenario.)
Airlines tend to accept far fewer risks than other forms of aviation.  The mission of an airline is to make money, and nothing interferes with that mission like the bad publicity & loss of assets (and potentially, certification) that comes from a crash.  In the military, there can be a mindset of accepting lots of risks because troops are counting on us completing this mission. In general aviation, there tend to be individual decisionmakers, with little institutional guidance & corporate wisdom to back them up.  But the airlines tend to be entirely willing to postpone a flight if it can't be performed safely, so for "airlines" to ignore V1 or other safety rules seems highly unlikely.  (Which isn't to say that an individual crew might not do so, although at least at US carriers, they aren't likely to continue to be employed if they're found out.)

--- EDIT, added in response to updates/edits in the original question:
What you're asking is, in essence, can "they" get permission to take off knowing that takeoff roll = available runway, and if anything goes wrong after the point at which stopping takes all of the remaining runway, then they're dead.  If takeoff roll = available runway, using all engines, after you've reached the speed at which you can no longer abort the takeoff within the remaining runway, and then you lose a motor, you now

Don't have enough runway left to stop, but also
You don't have enough runway left to accelerate to takeoff speed with the remaining thrust (less than the original case)

That's more or less the "bad guys storming the airfield" scenario, where you know that you're dead if you stay, so it makes sense to take off & hope that the motors keep running through the takeoff roll.  Given that the risk of staying is so high, the risk of losing an engine during those seconds of the takeoff roll is the lesser of the two evils.  And yes, in Viet Nam there certainly were times when C-130's would accept those sorts of risks to get the badly wounded out of dirt strips in combat.
Now, is that a reasonable thing to do in peacetime?  Not in my simple mind.  If we are assuming that the IL-76 crew did their performance computations correctly & their long roll was a known & accepted risk, then maybe they reached the opposite conclusion.  It's not something that I'd expect an airline to ever approve with passengers on board, and we'd have to get creative to find a scenario where they'd approve it for a ferry.
Can a crew make that sort of choice on their own?  Well, yeah, at least once.  Would an airline approve that option?  Hard to imagine.

+1 for bad guys storming the airport. I imagine a pilot slamming the throttles to max while bad guys carrying AK47s are running across the field.

As long as we are making up possible reasons, a couple that follow the rules but still end up there would be an actual engine failure (at V1 on a field limited takeoff) or windshear on takeoff which extended the takeoff roll.

@kevin On the other hand, it just might not be the best idea either if the bad guys carry man-portable SAM weapons. Even a short range SAM could make for a bad day. Then again in such a situation it might be worth it just taking your chances...

Just to add to the running commentary, it's also possible that the aircraft was incorrectly loaded (more weight than the pilots knew about), or even that they just never bothered to calculate their performance and assumed that it was "good enough".  That's the problem with this question, we really have no way of knowing.  (That being said, if I remember right, the story goes that the tower was recording the takeoff because this particular flight/operator was known for doing really stupid things so it may be more of a pattern....)

V1 is not a rule, it's a fact. You cannot ignore and you cannot get an exemption for it. V1 is the speed at which the remaining runway is too short for stopping the aircraft.
In other words: no matter what happens to your plane after V1, you have to take off. If a fire breaks out, an engine falls off, the windshield shatters, your flight computer dies, it doesn't matter. There simply is not enough runway left to brake, you must take off, climb out, and then you can figure out how to land again.
"Ignoring" V1, i.e. trying to abort a take-off after V1 simply means that you try to stop the aircraft, but will fail, so the aircraft runs off the end of the runway and bad stuff happens. The idea of "getting an exemption" from V1 doesn't make sense: basically, that means that all of a sudden out of thin air another couple hundred feet of additional runway magically appear. Which won't happen.

Not necessarily -- if you're accelerate-go limited on T/O performance (vs. accelerate-stop), you may have runway available in case of an abort after V1.  In fact, there are cases where you must abort after V1, for obvious reasons (like your elevators coming undone when you go to rotate).

V1 is a rule. If engine failure is not considered during takeoff V1 is not necessary.

@Andrius V1 is not a rule, in any sense of the definition. V1 also does not relate only to engine failures, V1 is the speed at which any reason that would cause you to abort a take-off, that the take-off can still be safely aborted on the remaining runway. For example blowing a tire, smoke in the cabin, etc. are all failures at which you can abort prior to V1 but not after.

@Andrius V1 is a rule of physics. After a given aircraft, with its current load and runway, at the current temperature and altitude reaches a speed that has been pre-calculated (for this set of conditions) and called V1, that aircraft in, those conditions will run out of runway (paved or otherwise), if the pilots attempt to abort the takeoff. Pilots are free to choose to abort the TO after V1, but it will, most likely, have disastrous results.


text:
What do firefighters do on ordinary days?
Some not very busy airports can have no even a minor incident for years and accident probably won't happen in a major airport during several decades. Training of course is done sometimes. I don't know how often though. This has to be the most boring or the best job if you wan't nothing to do. I think you can spend all your career without putting out single real fire or doing real rescue.
So what do firefighters do day to day?

I knew a, municipal in a small town, not airport, firefighter and he spent a lot of time organizing various things. Because they indeed had a plenty of time sitting around the station and doing whatever they wanted with the only limit that they had to be in the fire engines in 30 seconds if the alarm sounded.

https://www.faa.gov/airports/airport_safety/aircraft_rescue_fire_fighting/ - ARFF guidance a-plenty.

Spray water cannons over aircraft with retiring Captains. That keeps them busy a lot. :) https://en.wikipedia.org/wiki/Water_salute

@curious_cat Or first or last planes of that type in their airport.

@SMSvonderTann Yes. That too. Although not sure what exactly they spray when an air traffic controller retires. Apparently Wikipedia says for them too.  Mighty hard to reach the ATC Windows I suppose, eh?

Also, when the beancounters in the airport offices,  burn their popcorn & set off the fire alarms someone must respond. :) Actually not sure whether the city fire services respond or the airport's.

@curious_cat Maybe they just spray the controller directly when he walks out of the tower?

@reirab Yeah, after that, I think the controllers' union is opting out of the salute.:)

Calling them "firefighters" is accurate but they can respond to all sorts of incidents, not just fires (in the USA, even outside airports it's common for firefighters to respond to purely medical emergencies). On top of that, there's also training, maintenance and keeping physically fit.
This is from a firefighter at Hobart Airport in Australia:

The aviation firefighters do more than wait for airplane fires, they
  also attend to other incidents, such as motor vehicle accidents, fuel
  spills, hazardous material incidents and first-aid in the terminal.
[...]
"A lot of our working day is routine and there are different types of
  things that we need do every day regarding our equipment, servicing
  all of our equipment, checking it over ...," he said.

And this is from one at Heathrow:

We don’t really have an average day. We attend to all sorts of
  incidents. We attend to anything that is life-threating at the airport
  or on the roads around it; this could include a heart attack air or
  land-side, a drug mule incident where a passenger has transported
  drugs within their body and has ended up in a serious condition, or a
  car crash that we have to cut a victim out of.
We all have set duties to do every day and night including practical
  and theoretical training, testing and inspections, and cleaning of
  vehicles and equipment. The crews have to keep physically fit so we
  give them time for physical training and provide facilities to do
  this.

But how much they can attend other incidents? Most of the crew has to be ready on standby because if they are busy and not available airport cannot accept aircrafts and has to close until emergency services are ready for standby again.

a lot of the small regional airports where I live in france have the firefighters doing a multi task job. they handle baggage,fuel aircraft drive the vehicle with the steps to the aircraft and other jobs.


text:
How much does it cost if someone falls ill before take-off?
A month or so ago, I flew from LHR to Australia, via Doha, on a Qatar Airways A380. Just as we were about to enter the runway at LHR, the captain announced that someone had been taken ill on the plane, and we'd be going back to the gate. That delayed take-off by (I think) about an hour, and required topping up the fuel tanks.
How much would this have cost the airline? Are there any circumstances where they would pass the cost onto the passenger who fell ill?

Considerably less than once you're in the air.

Your question about passing costs to the passenger might get a better response on travel.SE.

they'd almost certainly pass the cost on to the passenger if (s)he were found to have been trying a prank rather than it being an actual medical emergency.

A medical emergency is an emergency for which the cost should not be a parameter in the decision process.

The cost is passed to the customers, but divided among all flight, not just the ones that had illness onboard.

@WayneConrad, actually the cost is divided among those who take future flights. Since the cost of this flight went up, the (thin) profit margin went down so future tickets will cost ever so slightly more to make up for it.

@ManuH, I never thought it would be a factor in the decision. I assume, however, that the airline has (self-)insurance, which impacts their costs. I could see a scenario where the airline's insurance company might want to pass the cost onto the traveller's insurance company. It'd be bad PR, but that's not stopped other airlines from doing stupid things.

@RogerLipscombe I do agree and was pretty sure you though like that. I wanted to add this warning (greatly improve by your mention of insurance) for newcomers without aviation safety culture.

@FreeMan, Actually... past, present, or future, these sort of things are just absorbed and baked into overhead as the cost of doing business. (i.e. Airline executives don't sit around and review individual instances and apply their specific cost overruns: "Gentlemen, John's Doe's little puking incident last week means we need to bump LAX to SEA by $11.37 per seat for the next 90 days to recover...") All customers pay a ticket price that hedges against incidents like this. Your correction of Wayne Conrad's comment wasn't really necessary. Just like this comment isn't really necessary... ;)

It's hard to get an exact figure, there are fuel prices, the time to taxi, gate charges, medical charges for the removal of the person on the plane, staff costs, and more. I can't guess at most, however from a fuel cost perspective I know for the 747-400 at LHR many airlines use a figure of 1000kg in planning for APU and taxi to takeoff. An A380 would be more, I'd ball park a figure of 1380kg for the airbus based on the MTOW difference (a rough approximation). 1380kg is about 1750 liters, at about .50 GBP per liter that's about 875GBP, or about 1150USD at today's conversions. So the fuel alone would cost somewhere around a grand, I'd imagine you could comfortably double that by the time all is said and done.
As for passing the cost on to the customer I've never heard of that being done for a genuine illness, or even a suspected illness. I don't know if they could if they wanted to, however I cannot imagine them trying it, the reputational fallout would be enormous.


text:
Could someone tell me what this part of an A320 is called in English?
I'm trying to understand a French document about the A320.
It's talking about a dual-input situation.
It says this:

Devant le pilote ayant pris la priorité, sur la partie supérieure du
tableau de bord appelée bandeau, un voyant vert s'allume dans le
cas où l'autre manche n'est pas en position neutre, signifiant ainsi
que l'autre pilote tente d'agir sur son manche.

A rough translation is:

In front of the pilot who has taken priority, in the upper part of the
instrument panel called the banner (??), a green light is lit if
the other controller is not in neutral position, meaning that the
other pilot is attempting to operate their controller.

Normally I'd expect bandeau in French to be "banner". Or it might be "strip". It seems to be a panel or something above the main part of the instrument panel containing the PFD. Just like to know if there is a specific term used by A320 pilots.

I think it's talking about the glareshield panel. It has many controls and buttons, including the dual input indicator.

This line is called the glareshield
The side stick dual input indicators are present on a part of the glareshield panel called the glare wings. These are present on both sides of the glareshield panel.
They look like wings.

I think the document is about this indicator present in the A320 glareshield panel. It's for dual input.

The upper part of the instrument panel is called the glareshield. It extends further out from the panel and therefore protects the screens below from glare.
Here is an overview of the A320 Instrument Panel (on the Captain's side):

(Airbus A320 FCOM - Equipment - Flight Deck)
The side stick priority light your quote talks about is located on the glareshield:

1 SIDE STICK PRIORITY lt
Red arrow light:

comes on in front of the pilot losing authority
goes out if he has recovered his authority [...]

Green CAPT and F/O lights:

Both lights flash when the pilots move both sidesticks simultaneously and neither takes priority.
When a pilot has taken priority by pressing the takeover pushbutton and the other pilot's sidestick is not at neutral, the light in front of the pilot with priority lights up. It goes out when the other pilot returns his stick to the neutral position.

(Airbus A320 FCOM - Flight Controls - Controls and Indicators)


text:
Burdens of working as an airline pilot
Every job in every industry has some "pressure", "stress", or "burdens" for that job. Being a PPL feels free, but I'm paying for flying. Working as a pilot, I get paid for flying. BUT, before I decide I want to join this industry, what are the burdens that an airline pilot has to face routinely? Does it vary if you're working for a small regional airline vs major international airlines?

You forgot the word "poorly" in there somewhere.

@CGCampbell yea? where?

I suppose @CGCampbell meant as in "poorly paid". I understood from other questions on this site that in North America wages are currently low especially in regional airlines. Situation differs a lot across the world so you can probably get good money in Middle East or Asia (if you can get at least 737 or A320 rating and are willing to move or live away).

This is a very broad topic and is heavily opinion based.
Vast majority of commercial pilots do love flying and that's the reason they go through the abuse by airlines. All GA pilots also love flying but either cannot afford the abuse or don't have time for it, so they just pay to satisfy this hobby.
So to answer your question, some of the burdens are:

High costs of training
Waiting a long time (2 years or more on occasions) before getting hired by an airline
Very low salaries in the beginning (several years)
Losing seniority (very often) when you go to another carrier
Staying away from home a lot
Very unstable industry
Many pilots eventually get bored and frustrated (regardless of initial enthusiasm)

Having said that, there are many many great benefits, too. The bottom line is that people only get into this career if they love it deeply.
The question you have to ask yourself is: Am I willing to undergo this trouble for my passion?

P.S.: The above holds true for the airlines and pilots in the US.

I believe it should be mentioned this is specific to North America. Middle East and Asia have shortage of pilots and therefore offer better wages and conditions. I heard 2nd-hand about pilots from Europe going to Middle East or Asia for much better money and in Europe the wages are a lot better than US.

@JanHudec True. I looked at FO monthly benefits for Etihad. US Airlines also pay the same but only annually.

Two more downside items: the possibility of losing your career because of medical problems and, if flying international routes, the stress of significant time zone changes.

The airline industry is projecting a serious pilot shortage in the US. In large part due to the drastically shrinking military pilot pool. Sorry I don't have a link to the article.

Ditto on "unstable". Never mind market swings, Major airlines must be the most mismanaged businesses ever. Gone are TWA, Pan AM, Eastern, Braniff. The carnage is stunning. Braniff bankrupted itself buying up routes. Carl Icahn was able to shred TWA because it was dying. Next time a major's CEO whines for a handout just say "Southwest". Oh, and unions have participated in the self-flaggelation, according to 1 insider's personal anacdote.

I know a number of current and former airline pilots and I would add "Stress on relationships".  Some of my airline pilot friends have been through multiple divorces as their spouses have drifted away and found other interests. No doubt this is partially a result of the "time away from home" item, but needs to be mentioned since it can have a direct effect on one's current and future earnings, ability to retire, retirement lifestyle, etc.

I always thought that the high divorce rate was due to the "fooling around with the flight attendants" problem. Now that the average age of flight attendants has skyrocketed, maybe that is no longer an issue.

Being an airline pilot in Europe myself, I can underline the above mentioned. The "work" itself is the way of becoming an airline pilot, not the flying later on. You need a long breath if it isn't successful at the first place. Flying is a service, so be prepared to spend your Off-days when others are at work. Or to leave the house when others are still asleep...

Pilots need to fly a certain number of hours each year if they want to maintain their flying privileges. Due to this, nowadays, some pilots pay airlines to hire them, so that they can fly. In France there even are petitions being created to make this practice illegal.


text:
Does Flight Following automatically include permission to fly through class C or D airspace?
The situation is as following - I requested flight following at approach, got a squawk and instructed to maintain VFR with heading and altitude at my discretion. My route is through class D and class C airspace for the altitude I chose. The question is - should I establish additional communications or report to the approach controller about flying through the class C and D airspace, or I am already permitted to do this?

Lets back up a minute and discuss what is required to enter C and D airspace.
For C and D airspace you must establish 2 way radio communications with tower or approach controller. Let's first discuss how this works if you are not taking Flight Following. As you approach Class C airspace you hail them and wait for a response, for example,

You: "Allentown Approach Piper 1234J @ 3000 en route to Queen City Municipal"
Controller: "1234J Squawk 1-3-5-2 and Ident"

Since the controller responded with your tail number you may enter the Charlie airspace (Delta has the same requirements).
Now when you are under Flight Following, ATC will coordinate a handoff to the Approach or Tower for the airspace you are about to enter, or ATC will say "radar services terminated," and you must contact the controller/tower yourself before entering.
You SHOULD NOT change frequencies until you are told to do so, since ATC may be trying to give you a traffic advisory. You can however tune your second radio (if you have one) to the approach/tower you are approaching, and begin to monitor traffic.

To amplify a point that is screwed up frequently where I fly: If flight following drops you or you're booted out of the IFR system (i.e. "If the controller says Radar services terminated") you are no longer in two-way radio communication with ATC and are not authorized to enter Class C and D airspace. (You're also not authorized to enter Class B airspace in this situation, obviously.) You must establish two-way communication with the controlling authority for that airspace on your own prior to entry.

Often the controller you're talking to will notify the tower or appch controller and approve a frequency change. Wonderful! But you have not yet established two-way comms with the right ATC and therefore have not met that requirement. Upon being approved for a freq change, attempt to contact the controller and if that fails (e.g. he's busy), avoid the airspace until two-way comm is established. If flying through controlled airspace the same applies; request a handoff from the controller you're talking to if he hasn't volunteered one, and don't enter until comms are established.

@voretaq7 your point about "Radar Services Terminated" is not quite true. To enter Class C, you must be in 2-way radio contact with the controlling authority. You can't call up, say, New York Center and then enter a Class C controlled by NY Approach. Once center hears your altitude & position, they will tell you "N69VT, contact approach on ..."  So even though you hear your numbers, that is not 2-way radio communications sufficient to enter the Class C because NY Center is not the controlling authority. It is the 2d phrase "Frequency change approved" that terminates your 2-way radio contact.

(con't)  The phraseology is "N69VT, Radar services terminated, squawk VFR, frequency change approved."  Perhaps your TRACON abbreviates it to simply "Radar services terminated"?

@hemp -- no, you do NOT need to be in 2-way contact with the new controller before entering Class C or D. the actual handoff has already been accomplished in the radar system, and the receiving controller has already accepted the handoff. that is sufficient.  I know these last comments sound like they are in contradiction, but you have to think about the way the entire system works. If the receiving controller cannot accept the handoff from the sending controller, the sending controller will drop you, and you are not allowed to enter.

@voretaq7 -- the controller may still want you in the Charlie even if he can't work you on radar (lets say the radar at his TRACON died while you were getting ready to shoot an approach -- kicking you out of the Charlie makes far less sense than simply reverting back to non-radar procedures).

@rbp -- That isn't guaranteed. if the controller you are talking to has handed you off then you're fine. But flight following is not the same as IFR, it's a secondary service, and a busy controller may not hand you off before you enter someone else's airspace as they're not required to. If that happens and you enter the airspace anyway, you are violating and you'll likely get a very unpleasant instruction from that controller to call and explain yourself. If I haven't been given a frequency change, I never assume I'm clear to enter. Usually I'll just call and request the change.

@hemp if the controller can't hand you off, he has to tell you, and then yes, you have to call the next controller before entering. what he can't do is not hand you off and not tell you.

@rbp -- I'll agree it is bad controlling technique to not notify me of impending encroachment on Class D, C, or B airspace. But ultimately as a pilot I cannot make any assumptions about a controller's use of good controlling technique when he or she is providing me with a secondary service. Unless someone can point to a very clear JO that states that it is the controller's responsibility, I will continue to assume it is mine.

7−6−11. TERMINATION OF SERVICE
Basic radar services should be provided to the extent
possible, workload permitting. Terminate radar
service to aircraft landing at airports other than those
where sequencing service is provided at a sufficient
distance from the airport to permit the pilot to change
to the appropriate frequency for traffic and airport
information (https://www.faa.gov/documentLibrary/media/Order/ATC.pdf)

also read 7−6−8. CONTROL TRANSFER. its too chopped up to quote here in a comment. Taken together, the controller is responsible for either telling you to contact the next controller or telling you he cannot.

As per JO 7110.65 ATC, Section 2-1-16 SURFACE AREAS, when you are in contact with ATC, you do not need to specifically ask for authorization to enter a towered service area:

b. Coordinate with the appropriate control tower for transit authorization when you are providing radar traffic advisory service to
an aircraft that will enter another facility's airspace.
NOTE-
The pilot is not expected to obtain his/her own authorization through each area when in contact with a radar facility.

Nice find. Wonder if it's anywhere on the pilot side of regs.

Very nice find. However, I would caution that "not expected to" is not the same as "not required to". As the pilot, you are still responsible for following the regs, and VFR Flight Following is different than being under IFR control. Flight Following is workload-permitted for the controller, and VFR traffic is lower-priority than IFR. As the pilot, if your route goes through Class C and you haven't been given permission to enter, I'd ask before I got there and not enter if you still haven't received clearance.

there is no such thing as "reciev[ing] clearance" through Class C.  If you are talking to ATC, and they are communicating your tail number, and you have not be told to stay out, then you have permission to enter. You don't need to be given explicit permission.

Sorry for the confusion on my part. No you don't need permission to enter C. B, yes, but C No. C I would still ping the controller before I got there. B I would ping the controller and stay out until cleared through.   After making a point of what you DON'T have to do, I kinda switched over to a "what WOULD I do" view.

Does this apply to VFR, IFR, or both?

IFR you are in positive control for the clearance you received so a second clearance isn't required.

Since you are already in radio contact with the ATC agency that controls the Charlie airspace (aka Approach), you are already allowed to enter it.
(If Approach doesn't want you in their Charlie, they'll say so: "N12345, remain outside the Charlie".)

To nitpick a bit, you don't actually need permission to enter the Class C airspace, just establish two-way communication. The controller has no say over what you do outside of his airspace. He can tell you "Don't enter", but you don't have to comply. You'd be foolish, not to, but you can enter anyway without violating any rules. However, once inside the Class C, if he says "Get out!" you have to follow his instruction. Class B is different. It requires permission to enter.

And to add irony to my nitpick, if you call the controller with your call sign, and he responds back with "N12345, remain outside the Charlie.", he has just established two-way communication with you and you are cleared to enter. Again, not wise, but you won't have violated any regs if you enter. Just angered ATC.

@shawn both of those are wrong. 91.123 (b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.

@rbp You are correct. Except outside of a Class C, the controlling authority has no control over the pilot. I said it was kind of a nitpick, but all you need to enter Class C is two-way comms. You don't need permission. That falls under the last part of your statement "....in an area in which air traffic control is exercised." However, once you enter the Class C, you are obligated to follow the controller's instructions.
Again, it would be unwise to pull that, but not a reg violation.

Air traffic control is exercised in all airspace classes except G, and also in towered class g airports.

Class E is primarily intended to separate IFR from VFR. A VFR pilot typically isn't under the control of ATC and isn't even required to have a radio in E. The only requirement for E is weather. Regardless, you don't need permission to enter C, just two-way comms. And a controller only has authority over you if you are in his airspace. Again, not wise to ignore ATC, but not illegal in this case.

@Shawn You are completely mistaken in all of the comments on this thread. 1. If you are given an instruction by ATC you must comply. So if you are told to stay out, you must stay out. 2. You can’t enter C or D airspace without establishing communication. Read the examples in the  AIM to clear up your confusion. 3. In Class E airspace  ATC keeps IFR traffic separate from other IFR traffic. If the conditions are VFR everyone is responsible for see-and-avoid.

@JScarry Good post necromancy, but please review my comments. There is no confusion. From a regulation standpoint, the Class C controller has NO authority over you until you are within the Class C airspace. You do not need permission to enter, just 2-way comms, as described above. Therefore, you CAN enter. But if he then tells you to leave, you have to follow his instructions. It's not a good idea to ignore ATC, but a pilot has broken no regs outside of the Class C. Feel free to ask the FAA. My point was, don't just take everything at face value. Actually understand the regs you follow.

Now if those regs have changed over the last 15 years, please point me to that change. When I was teaching, that was how ATC control authority was always defined. ATC can't control you outside of their airspace, and they probably aren't likely to even try, since they usually understand their limitations also. If they need you to do something that will affect their airspace, they'll likely request the change be made by whoever's airspace you're in.

You may not think you are confused, but you are wrongity wrong wrong wrong. You might want to read the comments on the accepted answer. If you are talking to ATC, they have authority over you. I take §91.123   Compliance with ATC clearances and instructions. literally.
(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. .

I ran across the Karas letter and thought it might be interesting to anyone following this thread, https://www.faa.gov/about/office_org/headquarters_offices/agc/pol_adjudication/agc200/interpretations/data/interps/2013/karas%20-%20%282013%29%20legal%20interpretation.pdf
"A pilot flying VFR in Class E airspace, which is controlled airspace, is not required to communicate with ATC; however, if a pilot is communicating with ATC and ATC issues an instruction, the pilot must comply with that instruction."


text:
How is minimum runway length related to V1?
1) Is $V_1$ used to determine minimum runway length? How is $V_1$ calculated?
2) If it is used to determine the minimum runway length, and for example we have a runway of 8000 ft and my airplane's accelerate stop distance required (ASDR) is 4000 ft and takeoff distance required (TODR) is 5000 ft, can my $V_1$ be as low as 15 kts? Since (let's say) below 15 kts, of course you will have the 4000 ft required to stop and also have enough distance to takeoff with 1 engine inoperative.
3) Let's say we have a very long runway so an airplane can make a rejected takeoff even at rotation speed ($V_R$). Can $V_1$ be the same as $V_R$?

Takeoff Field Length
The “FAR” Takeoff Field Length determined from the FAA Approved Airplane Flight Manual (AFM) considers the most limiting of each of the following three criteria:
1) All-Engine Go Distance:
115% of the actual distance required to accelerate, liftoff and reach a point 35 feet above the runway with all engines operating:

2) Engine-Out Accelerate-Go Distance:
The distance required to accelerate with all engines operating, have one engine fail at $V_{EF}$ at least one second before $V_1$, continue the takeoff, liftoff and reach a point 35 feet above the runway surface at $V_2$ speed:

3) Accelerate-Stop Distance:
The distance required to accelerate with all engines operating, have an engine failure or some other event at $V_{EVENT}$ at least one second before $V_1$, recognize the event, reconfigure for stopping and bring the airplane to a stop using maximum wheel braking with the speed brakes extended.

$V_1$ Speed
$V_1$ is the speed chosen by the manufacturer as "the pilot’s initiation of the first action to stop the airplane during the accelerate-stop tests."  Note that this is particularly important in that it is not a takeoff decision speed as some pilots like to think of it.  The decision must have been made prior to $V_1$ so that there is time to react by $V_1$.
This speed is chosen by the manufacturer and must be between the engine failure speed1 and rotation speed.  Within this range, they could choose any speed, but typically they choose the speed which gives a balanced field length (see next section).
There are also other factors to consider such as the maximum brake energy limit ($V_{MBE}$) which will prevent $V_1$ from being too high.

Balanced Field Length
If we takeoff from a fixed length runway (like, say one that matches the Takeoff Field Length from above), changing the $V_1$ speed will affect the weight that we can successfully continue the takeoff or abort within the available runway.
At a particular weight, a lower $V_1$ will enable us to stop sooner if we abort but will take more distance to continue the takeoff.  A higher $V_1$ will require more distance to stop but will take less distance to continue.  If we graph these values, there will be a point where the $V_1$ speeds for the abort/continue lines meet, and this is known as the balanced field length.  It is the value typically given in the AFM:

This is nice because it gives the pilot one important number to remember instead of different stop/continue $V_1$'s.
If they were to choose an extremely low $V_1$ as in your question, then it would require considerably more runway in order to continue the takeoff than if it were higher, and it would not be balanced.  Some AFM's do include separate charts for accelerate-go and accelerate-stop though so you could figure out exactly how much runway that you would need if the engine failed at a lower airspeed.

Rotation Speed
$V_R$ is determined independently from $V_1$, and if it is ever less than $V_1$ then it must be raised to be equal to $V_1$.

References
The regulatory information for takeoff performance on transport category aircraft is listed in 14 CFR Part 25, Subpart B, Performance, 25.101 - 25.113.
Of particular interest for this question would be 14 CFR 25.107 - Takeoff speeds and  14 CFR 25.113 - Takeoff distance and takeoff run
An easier to read document is the FAA's Pilot Guide to Takeoff Safety which covers this and a lot more.  Much of my answer was taken directly from this document, and I would highly recommend anyone that is flying a multi-engine aircraft to read the entire thing.

1 $V_{EF}$ itself must be above the minimum controllable airspeed on the ground plus acceleration while the pilot reacts to the engine failure.

Why must $V_R$ be strictly larger than $V_1$? Why not $V_1$ being reduced to $V_R$ (for instance)?

@Hugh It's a regulatory requirement, however within the range of allowable values, the manufacturer chooses $V_1$, so they could lower it if they wanted.   If they had to do that, it likely wouldn't be balanced though.

Just to make sure we're on the same page, I'll reiterate what should be obvious: $V_1$ is a speed at which you may stop in the available runway space or continue the takeoff.
In theory, $V_1$ could be any speed that matches this criteria -- it is not necessarily one speed. However, in practice we refer to a few different $V_1$ speeds:

Minimum $V_1$
Balanced $V_1$ (distance to takeoff is the same as distance to stop)
Maximum $V_1$

The reason why $V_1$ cannot be greater than $V_R$ is that you're already or about to be in the air. If you attempt to stop the aircraft rotating, you might be too aggressive and destroy the aircraft by tring to force the airplane down during or after rotation.
You also can't have a $V_1$ of something like 15 knots, as it may not be below $V_{MCG}$. If you did continue with full thrust on one engine at 15 knots, you would not have enough authority from the rudder to prevent the aircraft going off the edge of the runway, which is extremely dangerous. This is even more of an issue if you decide to continue the takeoff at $V_1$, which would almost certainly result in a runway excursion. Typical $V_{MCG}$ values for airliners can be above 100 knots, making your proposed situation impossible.
For all cases, using the balanced $V_1$ provides the minimum runway distance required, though company policy may require using a reduced $V_1$.

So the minimun value for V1 is Vmcg?
Thanks

@camilogv: yes, because if they continue the takeoff past V1 they risk having a runway excursion as they're below Vmcg.

Last question
When V1 is balanced, it is said to be BFL?

@camilogv: sorry for not getting back to you earlier. The V1 is always balanced if you are using a balanced field length.

@Qantas94Heavy: In that case, in an aircraft with some engines closer to the aircraft centerline than others, like a DC-10 (one engine under each wing, one mounted on the vertical stabiliser) or a 747 (one inboard and one outboard engine under each wing) could min-V1 for a failure of a centerline or closer-to-centerline engine be, at least theoretically, lower than min-V1 for a failure of a further-outboard engine?


text:
What do the numbers and letters mean in landing gear tire sizes?
I've got these two tire sizes: 27 x 8.5 R12 16 PR, H42 x 15.0 R21 26 PR. Can someone tell me what each of these numbers and letters mean?
Also, if the diameter of the rim of the wheel is not included there, is there a way to estimate it from those numbers?

Related

I've always wondered why this is called "landing gear", as the first use is for takeoff, and for some aircraft they are even dropped after takeoff.

@mins That might be an interesting question for English Language & Usage Stack Exchange. In German it its Fahrwerk (literally driving  gear), so the term is unrelated to landing. On the other hand, the French train d'atterrissage is also related to landing...

$
\begin{array}{|c|c|c|c|c|c|}
\hline
\textsf {(H) M x N} & \textsf{(R)} & \textsf{D} & \textsf{(PR)}
\\ \hline
\textsf {27 x 8.5} & \textsf {R} & \textsf {12} & \textsf {16} \; \textsf {PR} \\ \hline
\textsf {H42 x 15.0} & \textsf {R} & \textsf {21} & \textsf {26} \; \textsf {PR}\\ \hline
\end{array}
$

M: Nominal overall diameter
H: The same with higher percent of deflection
N: Nominal section width
R: Radial type
D: Rim size
PR: Ply rating code (static load that can be applied to the tire).

All dimensions in inches
Reference: Michelin and Dunlop.
Bonus: Tire manufacturing process


text:
What are typical CLmaxTO and CLmaxL values for modern aircraft?
Roskam gives these values for typical ranges:

However several of his tables are off (for example he estimates typical cruising L/D at 13-15 when many planes are above that). Does anyone know typical values for modern aircraft? For example, I'm guessing that values of 2.35-2.5 for takeoff and 3.2+ for landing might not be uncommon.

The following additional references.

Torenbeek chapter 7

Not a very new document, granted. But the list contains several jet transports with a $C_{Lmax}$ in landing of about 3 or over:

DC9-30 @ 2.98
B737-200 @ 3.05
BAC Three-Eleven @ 3.19
DC10-30 @ 2.98

2018 Sesar paper.. Linked article here, provided by @ymb1.

The table contains a computed value of $C_{Lmax}$ of the aeroplane in landing, based on dimensional data and published data.
The only thing to figure out now is which modern jet transports use triple slotted Fowler flaps with slats. In general, this won't be the case for shortened versions like the A319 and B737-700.
As mentioned in this answer, usually the longer/shorter versions all share the same wing, and only differ in length of the fuselage plugs. This means that the shorter versions have a lower wing loading, and don't need all the sophisticated flaps & slats to get airborne. As also mentioned in the question on B747SP flaps.

Funny table - "Flower" should read "Fowler".


text:
Do most commercial jets cruise at constant altitude/speed?
The weight changes throughout, so this means aerodynamics efficiency changes to maintain constant speed and altitude. Is this how most commercial jets cruise?

Related: What is weight-climb speed?

Yes, jet airliners cruise at constant speed and altitude. As fuel is consumed and weight decreases, the power required to maintain that constant speed and altitude is reduced.

The short answer is yes, although altitude changes may be sought for various tactical reasons during a trip.  The main thing that changes from weight reduction, from the pilot's perspective, is pitch attitude and thrust.
You usually file a cruise Mach number or TAS in your IFR flight plan (or at least the company operations dept does) and you fly that speed, more or less.  If under radar coverage, you have some discretion to go faster or slower, but generally you will fly at the flight planned speed (you have to notify ATC for changes of more than 5% of TAS or .01 Mach).
If outside of radar coverage (far north, or oceanic for example), it's critical to fly the speed in your clearance within the tolerance because it's critical to maintaining separation. But in any case, in general you have the speed bug on the tape set to some target speed or Mach number and you maintain that with thrust.
When in cruise, the autopilot is in altitude hold mode, so it just pitches the plane as required to maintain whatever flight level it's set to.  It doesn't care about anything else at that point. So altitude is held constant by the autopilot, and what happens is as fuel is burned off, pitch attitude will slowly go lower as less lift is required of the wings, pretty much imperceptibly, and speed will creep up with a constant thrust setting.
You're monitoring speed the whole time, and you will adjust thrust downward as required as speed slowly creeps up as your weight goes down, to keep the speed at the bug setting you've set (some airliners with autothrottle systems may do this part for you, as well as maintaining altitude).
Sometimes you'll fly through vertical air movement at altitude, like mountain wave, and if the wave you're in is going up, you'll observe the plane pitch over slightly to keep from climbing, and the speed creep up, and you have to reduce thrust accordingly to maintain bug speed.  If you run into down wave later, the opposite happens and you have to increase thrust.  Eventually you are out of the wave and back to the settings you started with.

Large commercial jets almost always fly IFR and thus are assigned altitudes they must hold so altitude is always constant.
There are no speed limits that practically apply to commercial aircraft at cruise altitudes (since there are no supersonic passenger planes left) so speed will vary a bit but many modern auto pilots are capable of speed holds so speed can be constant.
If a higher altitude is more efficient and the pilots have enough information to know that (winds aloft, local baro, etc) they can always request it from ATC but they may not simply climb to it on their own.

There was one famous exception to this rule. Due to how high it flew the Concorde was not assigned an altitude and was allowed to freely drift up as it burnt fuel and achieve maximum efficiency at all times. It could do this because there was no risk of it flying into another aircraft at the altitudes it cruised at.

Loved the typo of "aloud" instead of "allowed" with reference to the concorde. If theres such a thing as a freudian typo, that is it!

You based you answer on an ATC standpoint (altitude is constant because ATC asks us to maintain it), this is a bit misleading. The crew asked a given altitude which it optimal for their current weight, and will ask another one when enough fuel will be burnt to step climb to the next flight level (levels are quantized). I think this is what the OP wanted to clarify.


text:
Identify this older military-style prop plane?
I was watching a show and saw this plane and I was wondering if anyone would know what it is?

For context, it was on the show "Arrow" and the characters were flying to a fictitious island in the North China sea. From the scene I could see 2 pilot seats and some room for maybe 2 more riders in the cockpit.
The plane seemed mid to small for such a plane and the wing has a prop on each side and then some sort of attachment near the end of each wing.

Thanks for reading and for any ideas on what model it os, or where I could do some furhter research.
Regards,
-Brian

It's the same plane used in "con air"...

The "some sort of attachment near the end of each wing" are 450 gallon (1700 L) external fuel tanks.

The cockpit doesn't match the exterior shot: I'm not sure exactly what they used to film the interior, but it's not a C-123. I suspect it may be a mockup (a set - not even a simulator) but I could be wrong.

@TypeIA: Yeah, I think it might be a Boeing 737, actually. Wikipedia has a C-123 cockpit photo

The cockpit picture shows sort of a 737 flight deck. Someone else may see more, but on first looks, the displays are configured the wrong way round - the primary flight display ("artificial horizon" and lots of other stuff) should be outboard, while the nav display ("map") should be inboard on each side. Or am I confused now?

@CptReynolds Are those not multi-function displays (MFD)?  In that case, it's pilot's choice which instrument displays on which screen.  I know some Boeings use those, but I'm not a pilot, I just recognize things from programming training sims.  It might simply be they put the artificial horizon in a prominent location because it's the one instrument that even most non-pilot audiences will immediately recognize.

@DarrelHoffman yes, that's the cockpit of a 737NG (700/800/900 series).

@jwenting My point was that if those are MFDs, it might not be incorrect to have the displays configured the way they are, since the layout is customizable to suit the tastes of the pilots.  That said, I'm not sure there's much point to having three artificial horizons (2 MFDs and the smaller gauge) all visible at once...

The displays on the CDUs look oddly warped. As if they're actually printed cards which are sagging in the middle. That's why I suspected it might be a prop set instead of a sim (I think it goes without saying it's not a real aircraft as it would be unnecessarily expensive and cumbersome to film in one vs. a sim or set). It does look like a 737 layout though.

@DarrelHoffman 1st is for the captain, 2nd for the copilot, 3rd is a spare. Normally the 1st and 2nd are linked to different sensor sets, so if there is a sensor problem the crew can see that quickly because the 2 are out of synch.

@TypeIA My favorite prop-error I've seen like this is when you can see the altimeter in the shot and it clearly shows that they were on the ground when it was filmed, or the throttle is all the way off or something.  (I actually took part in one such film shoot for an educational film as the copilot - on a retired C-123 with no engines - they did tell us which switches and levers to pull to make it look realistic, and we faked the gauges in post.)

@DarrelHoffman Absolutely! Another trope is the wildly spinning altimeter during a crash sequence. This is sometimes faked by just spinning the adjustment knob. You can see the setting in the Kollsman window spinning. For example, the Ford Tri-Motor crash scene in Indiana Jones and the Temple of Doom.

Fairchild C-123 Provider. Also appears in "Air America" (1990) and "Con Air" (1997).

The type also appears in "Outbreak" (1995) as the bomber that's sent to bomb Cedar Creek. I'm not sure it's the same airframe.


text:
What options are there in Canada for treatment of severe depression and anxiety for pilots?
I'm a Canadian commercial helicopter pilot, and I've been struggling with severe depression and anxiety issues since childhood.
I'm very good at faking it, well, good enough that I've been able to lie on my medical in order to get it. Initially I had a 'good reason' to, I thought that my depression issue had something to do with not being fulfilled in life and that maybe following my dreams would sort it out. Because that was the only thing I hadn't tried yet, besides chemical treatment.
Well, it hasn't. In fact, its become abundantly clear to me that its entirely a chemical issue. Its not an issue of environment, job, friends, family, its not an issue I can talk about because there is no reason in the first place. I need actual prescription treatment.
It's entirely independent of my life, which I have no complaints about. Gradually its gotten worse. I took myself off of flying duty when the suicidal ideaton started up again, and have been unemployed since as I cant even get out of bed before 4PM most days, not fit to fly in the least.
Ever since then I've been treating it with cannabis, which has had quite satisfactory results, the daily life-is-pain levels have descended from a steady 8 to a solid 4. But as everybody knows that's not sustainable with aviation drug tests, as well as obviously illegal to continue. I've done lots of research into my options for treatment that wont end up throwing my career away, but maybe its just the depression talking, but all of them see like rather optimistic and shit gambles to me. Every non chemical option i.e, shrinks, supplements, getting outside, exercise, has fallen flat entirely. TC does say on their site that they have some program for treatment, but my interpretation of it is that the goal is to have you off the medication before returning to flight, not to have you able to stably take it during, which in my case sounds like a recipe for disaster as I feel it'll just come back.
I'm seriously considering just hanging up my helmet for good and just accepting that until the issues are sorted out fully, which may be never, that I'll have to pursue another career. I don't want to, I want to be a pilot. I don't want to be a washed up former pilot, because I don't know if I'd ever get over that. But I'm killing myself slowly doing it, so I have to do SOMETHING.
Has anybody ever faced a similar situation before, or have any ideas?
Because all I can see options wise right now is; A, throw away tens of thousands and an entire career to get treatment, and possibly never get over that. Or, B, continue lying on the medical and keep going, but effectively torturing myself.
I don't know what I'm expecting asking an anonymous forum this, but I don't have anyone else to ask aviation related questions and I despise working with shrinks.
PS:
Also, don't be that guy, or any variant of that guy, who goes, "Well you shouldn't have become a pilot in the first place then!", because there's always that guy. I know. Tell me when you've got a time machine to make that piece of advice worth anything.

Having lied on your medical forms, for what sounds like a significant length of time and to a significant degree, you're in a situation that probably nobody here is qualified to advise you on, beyond the obvious plea to get help & get clean before you touch an aircraft again. An attorney with some specialization in aviation medicine may be needed to untangle the issues you'll have when presenting your history to a treating physician, who may be compelled to share that with an AME or a government authority. This is beyond that the internet can advise you on.

Also, in the US at least, lying on the FAA Medical form is a felony offense that can land a pilot in jail, along with loss of all certificates. So please don't plan on continuing that path as a solution, and be very, very suspicious of anyone peddling that advice.  I wouldn't try to guess what good solutions may be available for you, but spending your life one revelation away from going to prison is most certainly not an viable plan.

I don't have an easy answer for you but I do want to say - it may be better to have a mildly fulfilling life doing something else while being mentally healthy, than to sacrifice your health to fly only to continue being miserable, and worst of all possibly harming yourself.

For what little it's worth, I'm not a washed up former pilot, but I am a washed up former software developer. I tried for literally years and years to make my "preferred career" work for me before I finally decided it just wasn't working out. So I started over in a completely different career path, and I've never been happier. I'm not saying that changing careers may cure your depression, but I am saying that sometimes a career change is the best option, even if you've invested a hell of a lot in your current career.

Where exactly did you read that TC has the goal to get people off their medication before returning to flight? I've skimmed the official TC handbook for aviation medical examiners at https://tc.canada.ca/en/aviation/publications/handbook-civil-aviation-medical-examiners-tp-13312#psychiatry-ssris, and while I have to admit I didn't read ALL of it, I did not get the impression that your assumption is the case. In fact, they make explicit mention of new medication have fewer and less intense side effects that do not appear to overly hinder pilots.

I'm not going to address the legal aspects of your question, but I will tackle the psychological side as I have a degree in it - although I'm not a practicing psychologist. It sounds like you have been through a bad period and are likely coming out of it into a better period, what you need to do is see a professional and get some help very soon. Everything seems impossible when you're suffering depression, but it's very treatable and you may still be able to fly.
It's in everyone's best interest, especially yours, to have you well and functioning. As you have stated yourself going without treatment is unsustainable whether you are flying or not, so there's two possible outcomes with treatment:

You're better and you can still fly: pilots can fly on anti-depressants in most jurisdictions, including Canada, provided they get medical clearance
You're better and you do something else

Either outcome you're better, which is miles ahead of where you are now. You lose nothing by getting treatment, things can only get better with it.
Drug treatments exist for most types of depression and bi-polar type disorders, and studies show that they are most effective when they are paired with counseling. I would suggest cognitive-behavioral therapy (CBT) as you will learn better coping strategies and thought patterns. Things will get better if you get help, so see your doctor right away.

This sounds very much like what my wife—who is a practicing psychologist—would recommend, down to the recommendation of CBT.

GdD gave good advice, take it. It is also pretty much as far as any advice can go in a setting such as this, or any non professional exhange for that matter, believe me. Each mental condition is unique, and while I understand the request for experiences of peers, however sincerely they are given they may only lead one astray. Go for professional help.
Having said that I'll share with you (and the rest of the internet) a few thought of a case with some similarities to yours. Remember: the following is not advice, do not draw any parallels or conclusions, let alone make decicions based on it. It is just a story of how stuff went (and still does) with someone.
You have obviously seen, that depression is a peculiar thing. It does not need to arise from any obvious source, and when it presents itself with no apparent reason, say, in a situation of life that is perfectly fine otherwise, it can be, paradoxically, horribly crippling. The loop one gets into in a situation such as that is quite unbrakeble alone and with reasoning. Help of the surrounding people cannot penetrate that wall, and at worst, the "helping" uttarances are like shoutin "swim" to a person sinking into quicksand.
Now: therapy itself in this particular case was not a direct answer or cure, and one wonders if it ever is. Not helping was the fact that the subject was highly reluctant to "go see a shrink". Finding a therapist that did not piss off in one way or another was tough enough, and the search apparently still continues, but at least the sessions in the end were able to give enough help to the wandering mind, to get a hint of what things were about. Took years though, with ups and downs and at least three diffent professionals, but eventually the subject oneself was able to figure out the main reasons for reoccuring depression, sort of gaining the ability to observe oneself from the outside when things were tough. At times, still, the subject does suffer  depression, during which the perspective on life still does get distorted, but the frequency and depth are tolerable.
At start of the exploration into therapy, as there was no apparent comprehensible reason to be found for the depression, a fear of maddness, so to speak, was settling in. The somewhat akward therapy sessions were able, however to let one see what probably is the problem, and address it as much as possible. The person in question is very socially talented, being able to navigate pretty much any situation at will. Unfortunately the person is also extremely introverted, so in this case utilizing ones most proficient skill is also the most exhausting exploit. Surely avoiding social interaction alltogether is not a very viable option, but understanding the reason for paralyzing energy drain helped block most of the leak.
A sideplot in this story is of course aviation. A career and hobby goal, which, no surprise, was pretty much doomed from the beginnig for reasons made clear above, and seriously adding to the depression and anxiety along the way. Much in the same manner as using social skills to advance in life, which in turn was burning all the resources needed to support that life, this goal of aviation was pursued obsessively, further adding to the drain. Being absolutely truhtful, licences should have been unobtainable for this person because of the hardships experienced.
When it became obvious that aviating was no longer possible (actually depression was not the prime reason for that), the prime reaction was clearly that of relief. I suspect the person probably actively pushed the matter into background to let it soak in, making it look less of a blow than it actually was.
Now, eons later, the subject of unfulfilled dreams still obviously pisses off, but age clearly brought some help along the way. You see as days go by, less and less thing are possible. To survive one will adapt, do different things, and be proud of what got done in the younger years. Realizing that one should not let what one does define one, or that desperately hanging on to something, however deeply one (at least thinks one) loves it can be utterly destructive. At least in this case it almost was. For this person, there is life after aviation. It's not what the person thought to have subscribed for when younger, but it's ok enough to push on.
I hear this person say often, that the meaning of life is not to become what you want to be, but to become what you are.
I'll leave you with that thought. It may be just a mantra to keep oneself happy, (or happier) but at least in this case it seems to work, for whatever reason.
P.S. this "answer" may get deleted as it really is no answer according to ASE standards. I may also delete it myself, for no particular reason.